1. Field of the Invention
The present invention relates to a fixing temperature control device which is applied to a fixing device in an image forming apparatus such as an electrostatic copying machine or a facsimile for carrying out on-off control of a heater for heating a fixing device.
2. Description of the Related Art
Generally in an image forming apparatus, for example, a copying machine, an electrostatic latent image formed on a photosensitive drum is developed into a toner image and the toner image is transferred onto paper sheets, after which the transferred toner image is heated and fixed by a fixing device. The fixing device comprises a pressure roller and a heat roller heated by a heater for heating and fixing toner particles to the paper sheets passing between both the rollers.
In order to heat and fix toner particles, the temperature of the fixing device must reach a predetermined temperature. If the temperature of the fixing device is lower than the predetermined temperature, toner particles are insufficiently fixed. If the temperature of the fixing device is higher than the predetermined temperature, so-called high-temperature offset occurs. The high-temperature offset is when that toner particles which enter a molten state due to high temperatures remain on the pressure roller or the like and are transferred onto unnecessary portions of the paper sheets. Specific examples include duplicating.
Conventionally in the copying machine or the like, energization control (on-off control) is continuously carried out with respect to a heater for heating a heat roller from the time when a power supply switch is turned on to the time when it is turned off, to warm the fixing device to a predetermined temperature.
However, it is not preferable in terms of energy saving to warm the fixing device when copies are not made.